This invention relates to steel rod rolling mills of the type where hot rolled rod is directed from the last mill stand through water cooling boxes to a laying head which forms the rod into a series of rings. The rings are collected on a moving conveyor in a non-concentric overlapping pattern where they are subjected to further controlled cooling to obtain desired metallurgical properties.
As illustrated in U.S. Pat. No. 3,469,798, the laying heads can be either of the vertical, horizontal or inclined type. Although vertical laying heads provide a more consistent ring pattern on the conveyor, they suffer from the disadvantage of requiring traction devices to direct the rod along a downwardly curved path from horizontal to vertical. Examples of such traction devices include chain guides of the type shown in U.S. Pat. No. 3,100,070 and wheel guides of the type shown in U.S. Pat. No. 3,777,964. These traction devices are mechanically complex, and as such are difficult and costly to maintain, particularly under the demanding conditions which prevail in modern mills, where the rod is being delivered at speeds exceeding 70 meters/sec. and at temperatures in the range of 780.degree.-1000.degree. C.
In the past, there have been occasions where after the rod has been turned downwardly, pinch rolls have been employed to drive the rod tail ends through vertical laying heads. Some thought has been given to substituting similar pinch roll arrangements for the conventional traction devices used in advance of the vertical laying heads. However, those skilled in the art have felt constrained from making this substitution because of a belief that pinch rolls cannot be relied on to supply an uninterrupted driving force at the critical time when the rod front end is negotiating the curved path from horizontal to vertical. The basis for this belief is that if the pinch rolls are opened to accommodate an easier entry of the rod front end, then there will be insufficient time available to re-establish a steady-state roll nip before the front end encounters the resistance of the downward bend into the laying head. Alternatively, if the pinch rolls are closed to their normal operating setting prior to the front end coming through, then the impact of rod entry will force the rolls to jump apart momentarily, thus again making it doubtful that a steady-state nip can be re-established in time to drive the rod front end downwardly into the laying head. The present invention provides a different method and apparatus for employing pinch rolls which avoids these difficulties, thereby making it possible to do away with the more complex traction devices conventionally employed to drive rod along downwardly curved paths into vertical laying heads.